Despite the fact we routinely encounter moving auditory stimuli in our day-to-day environment, very few data exist describing or explaining the auditory system's response to moving sounds. The major aims of this grant application are (1) to obtain some basic psychoacoustic data relating to auditory motion perception in normal-hearing observers listening both binaurally and monaurally (one ear occluded); and (2) to gain a better understanding of the mechanisms underlying human auditory motion perception. A series of experiments will be conducted in a free-field (anechoic) environment, employing a horizontally rotating loudspeaker system for stimulus presentation. Standard psychophysical procedures will be employed requiring subjects to make simple button-press responses to indicate their detection or perception of the particular stimulus condition under study (e.g., the presence of motion, the direction of motion, the relative velocity of a signal, etc.). Among the specific questions addressed are (1) What is the threshold rate for detectability of movement? (2) Is motion perceived directly by the auditory system, or is it inferred from prior discrimination of spatial and temporal positions? (3) Do direction-specific motion analyzers exist in the auditory system? (4) Are there interactions between visual and auditory perception of motion? Results from the proposed experiments would hopefully contribute to our understanding of how the human nervous system responds to auditory signals that are in motion, and of how the auditory perception of motion affects or is affected by visually perceived motion. From a practical standpoint, it is of concern to discover the degree of handicap (in terms of auditory spatial and motion perception) suffered by monaural listeners in a dynamic auditory environment. Assessing the severity of such handicaps might have important implications for the rahabilitation of hearing-impaired individuals, including both unilaterally impaired persons who usually use a single aid.